Automatic headlamp dimmer



Oct. 4, 1966 c. w. MILLER AUTOMATIC HEADLAMP DIMMER Filed Feb. 8, 1962 ATTORNEY United States Patent Delaware Filed Feb. 8, 1962, Ser. No. 171,850 8 Claims. (Cl. 315-83) This invention relates to automatic headlamp dimmers and particularly to a time delay for automatic headlamp dimmers.

There are in use on automotive vehicles headlight dimmers including a light sensitive element with appropriate electrical circuitry for switching on the low beam headlights of a vehicle when the light sensitive element is exposed to bright lights such as encountered in city driving or when meeting an oncoming vehicle and to switch on the upper beam headlights when the light sensitive element is exposed to a light intensity below a predetermined level. Such automatic headlight dimmers are usually equipped with means to control the sensitivity of the circuits so that the headlights are not switched from one beam to the other when the incident light intensity undergoes a very short transient change of intensity. However, it has been found that when the upper beams are in use and the vehicle is exposed to light from overhead fiashers or reflective objects near the edges of the road, the automatic headlight dimmer will dim the headlights despite the absence of any oncoming vehicles. Therefore, it is desirable to provide a time delay feature on the dimming cycle to reduce or eliminate the unnecessary and unwanted dimmings. On the other hand, it is essential that the time delay does not cause a substantial delay in the change from low beam to upper beam lights since a rapid response in that direction is often essential for proper visibility.

It is therefore an object of this invention to provide an automatic headlight dimmer having along time delay in switching from the upper beams to low beams. It is a further object of this invention to provide an automatic headlamp dimmer having a relatively long time delay in changing from upper beam to lower beam and having a relatively short time delay in changing from lower beam to upper beam.

This invention is carried out by providing an automatic headlamp dimmer having a time delay capacitor in circuit with a variable impedance whereby the impedance has one value during high beam operation and a different value during low beam operation.

The above and other advantages will be made more apparent from the following specification taken in conjunction with the accompanying drawing which is a schematic circuit of an automatic headlight dinner according to the invention.

As illustrated in the drawing, the automatic headlight dimmer circuit comprises a phototube 10 connected to a grid of the preamplifier tube 12 which in turn has its plate 14 connected to the grid 16 of an amplifier tube 18. The output of the amplifier tube 18 is connected in series with coil 20 which controls armature 21 of a sensitive relay 22. When the coil 22 is deenergized armature 21 touches contact 23 to connect a power relay 24 to a power supply line 25. The power relay 24 has an armature 26 connected to the vehicle power supply and movable between a pair of contacts 28 and 30 which are connected to the upper and lower beam lights, respectively.

Electrical power is supplied to the automatic headlight dimmer from a power supply by conductor 25. The supply voltage is nominally about 13 volts, but tends to fluctuate slightly according to the condition of the vehicle battery, etc. To provide a regulated voltage for control of the electronic circuitry, a ballast tube 34 in series with a voltage divider is connected between the conductor 25 and ground. The voltage divider comprises resistor 36 in series with a variable resistor 38, both of which are in parallel with resistor 40. Preferably, the variable resistor 38 is adjusted so that the voltage on line 41 at the junction of the ballast tube 34 and the voltage divider is 8 volts. The action of the ballast tube will maintain this voltage indipendently of variations in the power supply.

A second voltage divider comprising resistors 42, 44 and 46 is connected between the regulated voltage line 41 and ground. The filament 48 of preamplifier tube 12 is connected to the point between resistors 42 and 44 while the cathode 50 is connected to a variable tap on resistor 46. The grid 72 of the preamplifier tube 12 is connected to phototube 10. The plate 14 of the preamplifier 12 is connected to the grid 16 of amplifier 18 and is also connected through a load resistor 74 to the regulated line 41.

Another voltage divider comprising resistors 52 and 54 is connected between the regulated line 41 and ground and resistor 52 has a variable tap which is connected to a high value resistor 56 which in turn is connected to the grid 58 of preamplifier tube 12 to control the sensitivity of that tube. Filter condenser 60 is connected between the grid 58 and ground. The grid 58 is also connected through a variable resistor 62 to a stationary contact 64 on the sensitive relay 22. When the armature 21 of the sensitive relay is pulled against contact 64, then the variable resistor 62 is connected through the coil 68 of the power relay 24 and its parallel resistor 70 to ground thus changing the voltage on grid 58 and changing the sensitivity of the preamplifier. The effect of this arrangement is to provide one sensitivity when the high beams are on and a greater sensitivity when the low beams are on. Then the high beams will be turned on at a lower intensity level of illumination than that at which the low beams are turned on.

A voltage divider comprising resistors 76, 78, and is connected between the regulated line 41 and ground and a variable tap on resistor 80 is connected to the cathode on amplifier tube 18. Thecathode is also connected to a normally openoverride switch 82 which in turn is connected to ground. This switch 82 may be closed manually to render the automatic dimmer inoperative when manual dimming control is desired. Both the filament 84 and the grid 86 of amplifier tube 18 are connected to the power supply line 25. Preferably the circuit is designed so that the voltage at the junction of resistors 76 and 78 is 6 volts, the variable tap of resistor 80 can be adjusted to 3 volts, and the plate of amplifier tube 18 will operate at about 6.5 volts when the tube is conducting. Of course, the plate will rise to the full voltage of the supply line 32 when the tube is not conducting. A time delay capacitor 88 of about 1000 mid. is connected between the plate of amplifier 18 and the junction of resistors 76 and 78. A second capacitor 90 of about mfd. is in parallel with the coil 20 of sensitive relay 22 to absorb the current surge of the coil 20 when the current supply to the relays is interrupted.

In operation, when the phototube 10 is exposed to low intensity incident light it will have a very high resistance and the preamplifier tube 12 will be biased to a nonconductive state. Then, since there is no current flow through load resistor 74, the full 8 volts of. the regulated line 41 will be applied to grid 16 of amplifier tube 18, causing that tube to conduct. Current will flow from power supply line 25 through coil 20 of sensitive relay 22 and the tube 18 to ground thereby causing the relay armature 21 to be pulled against contact 64 as shown. There is then no voltage supply to the power relay coil 68 and the armature 26 will remain connected with stationary contact 28 as shown to energize the upper beam filaments.

When phototube is exposed to high intensity light, its resistance will become very low and will tend to bias the preamplifier tube 12 to its conductive state. The voltage of plate 14 of the amplifier will then drop very close to the cathode potential and this voltage will bias grid 16 of amplifier tube 18 to cause the latter to stop conducting. Then the sensitive relay 22 will become deenergized, causing the armature 21 to move up against the upper contact thus energizing the power relay 24 moving its armature 26 against the lower contact 30 to deenergize the upper beam lights and to energize the lower beam lights. However, due to the time delay capacitor 88, the sensitive relay 22 cannot be deenergized instantly, but rather, after the amplifier tube 18 stops conducting, current will continue to flow from the power line 25 through the relay 20, capacitor 88, and resistors 78 and 80 to ground until the capacitor 88 becomes charged to the potential of line 25.

It has been found in practice that the average time for the headlights to switch from upper to lower beam after the bright light is impressed on the phototube is about 1.2 seconds whereas when the time delay capacitor 88 was omitted from the circuit, the switching time was 0.2 second. When the bright illumination is removed from the phototube 10 and the amplifier 18 begins to conduct, the time delay capacitor 88 rapidly discharges through the conducting tube and resistors 80 and 78 so that the current through the sensitive relay coil 20 will begin without an appreciable delay.

It is thus seen that this invention provides a time delay on the dimming cycle by the mere addition of a single capacitor to an otherwise conventional circuit and yet does not present an undesirable time delay when the lights are returned to upper beam. This selective action of the time delay capacitor 88 is due to the fact that it is, in eifect, connected in parallel with a variable impedance,

i.e., the amplifier tube 18. When the amplifier tube ceases to conduct, the voltage on the plate tends to rise to the voltage carried by the power supply line 32, say 13 volts, but this voltage rise cannot take place until the capacitor 88 is charged through the relatively high impedance circuit including the relay coil 20. However, when the tube begins to conduct, the capacitor 88 discharges through the relatively low impedance of the amplifier tube and resistors 80 and 78 so that the voltage of the amplifier plate can drop almost immediately.

The embodiments of the invention disclosed herein are for illustrative purposes only and the scope of the inven tions is intended to be limited only by the following claims.

I claim:

1. An automatic headlight dimmer comprising an amplifier having output terminals, said amplifier including variable impedance means, light sensitive means for solely controlling the impedance of the amplifier, relay means connected to the output terminals for controlling the headlights, and capacitor means connected across the output terminals for delaying the voltage increase thereacross when the impedance is increased.

2. An automatic headlight dimmer comprising an amplifier, said amplifier including a vacuum tube having output terminals, light sensitive meansfor controlling the conductivity of the vacuum tube according to the incident light intensity, relay means connected to the output terminals for controlling the headlights, and capacitor means connected across the output terminals for delaying the voltage change thereacross when the vacuum tube conductivity is decreased.

3. An automatic headlight dimmer comprising an amplifier, said amplifier including a vacuum tube having output terminals, light sensitive means for increasing the impedance of the vacuum tube when said means is exposed to bright light, relay means connected to the output terminals for controlling the headlights according to the intensity of light incident on the light sensitive means, and capacitor means connected across the output terminals for delaying the voltage change thereacross when the impedance of the vacuum tube is increased.

4. In an automatic headlight dimmer, a photoelectric element responsive to incident light, a preamplifier connected to the photoelectric element for amplifying the output thereof, an amplifier controlled solely by the preamplifier, the amplifier having output terminals, a headlight controlling relay controlled by the amplifier, and a capacitor connected across the output terminals for delaying the voltage change thereacross when the amplifier impedance changes.

5. In an automatic headlight dimmer, a photoelectric element responsive to incident light, a preamplifier connected to the photoelectric element for amplifying the output thereof, an amplifier controlled solely by the preamplifier, the amplifier having output terminals, a headlight controlling relay controlled by the voltage of the output terminals, and a capacitor means connected across the output terminals for imposing a relatively large time delay on the voltage change thereacross when the amplifier impedance increases and for imposing a smaller time delay on the voltage change when the amplifier impedance decreases.

6. In an automatic headlight dimmer, a photoelectric element responsive to incident light, a preamplifier connected to the photoelectric element for amplifying the output thereof, an amplifier tube controlled solely by the preamplifier, the amplifier tube having output terminals, a headlight controlling relay controlled by the voltage of the output terminals, and a capacitor means connected across the output terminals for delaying the voltage change thereacross when the amplifier tube ceases to conduct.

7. In an automatic headlight dimmer, a photoelectric element responsive to incident light, a preamplifier connected to the photoelectric element for amplifying the output thereof, an amplifier tube controlled solely by the preamplifier, the amplifier tube having output terminals, a sensitive relay controlled by the voltage of the output terminals, a headlight controlling relay controlled by the sensitive relay, and a capacitor means connected across the output terminals for delaying the voltage change thereacross when the amplifier tube ceases to conduct.

8. In an automatic headlight dimmer,'a photoelectric element responsive to incident light, a preamplifier connected to the photoelectric element for amplifying the output thereof, an amplifier tube controlled by the preamplifier, the amplifier tube having output terminals, a sensitive relay controlled by the voltage of the output terminals, a headlight controlling relay controlled by the sensitive relay, and a capacitor connected across the output terminals for substantially delaying the voltage change Ehereacross only when the amplifier tube ceases to conuct.

References Cited by the Examiner UNITED STATES PATENTS 2,560,748 7/1951 Silva 315-83 2,615,079 10/ 1952 Pardue 3 l7142 2,872,618 2/1959 Matkins 31583.1 2,890,387 6/1959 Wiley 31583.1

JAMES W. LAWRENCE, Primary Examiner.

GEORGE N. WESTBY, DAVID J. GALVIN,

Examiners.

L. D. BULLION, S. A. SCHNEEBERGER,

Assistant Examiners. 

